[Solubility Measurement] Considerable prior art exists regarding the measurement of the solubility of a material by performing experiments, e.g. dissolving an amount of a substance in an amount of a solvent system to test the solubility of the substance in the solvent system. A number of parameters may be varied, such as the temperature at which the experiment takes place, the ratio of the amount of substance to the amount of the solvent system, the duration of the experiment, the method of agitation used to obtain a homogeneous mixture of the substance and the solvent system e.g. stirring or shaking, the workup method e.g. centrifugation, and the analytical techniques used to determine the amount of dissolved material.
[Turbidity Measurement & “Optical Parameter”] Further, the prior art comprises a number of methods for assessing whether a substance has been fully dissolved in a solvent system by measuring an optical parameter of the sample. This optical parameter is related to the amount of suspended solids present in the sample. This may involve measuring the attenuation, by means of scattering or absorbance, of a beam of optical light directed through a portion of the sample. Alternatively, this may involve measuring the intensity of scattered light at a detector placed at an angle to the optical light source directed through a portion of the sample. Furthermore, one or more light beams and one or more detectors may be used. Optical light is understood to include the infrared, visible or ultraviolet regions of the electromagnetic spectrum. Alternatively, the quantity of dissolved material may be determined by removing a portion of the sample and analysing it gravimetrically or by using spectroscopic or ultrasonic methods. The quantity of dissolved material may also be determined in situ using spectroscopic or ultrasonic methods or electrozone sensing.
[“Solubility Curve” And “Metastable Zone”] Solubility and metastable zone width curves are known as a method for summarising and graphically representing the range of conditions under which crystals will grow and those conditions that will result in primary nucleation. FIG. 2 depicts an example of a solubility curve and the corresponding metastable zone. In FIG. 2, the temperature TEMP is on the horizontal axis and the concentration of the material CONC is on the vertical axis of the graph. The line indicated by SOL in FIG. 2 is the solubility curve. A solubility curve indicates the solid-liquid thermodynamic equilibrium concentration of a substance in a solvent system, as a function of temperature. It is also referred to as the clear point curve in the prior art, as it can be obtained experimentally by heating a slurry of material in a solvent system until complete dissolution is obtained, resulting in a clear solution (the clear point). Crystals will grow at concentrations above the solubility curve. The line indicated by MSZ in FIG. 2 is the metastable zone boundary. The metastable zone boundary indicates the concentration of a substance in a solvent system above which primary nucleation occurs, as a function of temperature. It is also referred to as the cloud point curve in the prior art, as it can be obtained experimentally by cooling a saturated solution at a fixed rate until nucleation occurs and the solution becomes cloudy (the cloud point). At concentrations above the metastable zone boundary, spontaneous crystallisation, i.e. primary nucleation, will occur.